Exploring, drilling and completing hydrocarbon and other wells are generally complicated, time consuming, and ultimately very expensive endeavors. As a result, over the years, a significant amount of added emphasis has been placed on well monitoring and maintenance. Careful attention to design, monitoring and maintenance may help maximize production and extend well life. Thus, a substantial return on the investment in the completed well may be better ensured.
Monitoring well conditions may be undertaken by way of running a logging application. That is to say, logging to determine well pressures, temperatures, flow rates and other profile characteristics may be undertaken over the course of the life of the well, and not just prior to well completions. However, such follow-on logging comes with considerable costs. For example, in order to run such applications, the well may be shut down and other applications put on hold for several hours, if not days, while the logging application is run. Depending on the particular well and operations suspended for the logging, this may translate into tens to hundreds of thousands of dollars in added costs, particularly when factoring in lost production time.
Due to the high costs associated with follow-on logging as described above, ongoing monitoring of well conditions is often attempted through the use of downhole structure that is already present in the well. For example, pressure, temperature and other sensors may be incorporated into the sidewalls of completions tubulars. These sensors may be communicatively tethered to surface equipment via a line running along and supported by the tubular structure. Thus, data acquired by the sensors may be relayed to the surface equipment for ongoing monitoring of downhole well conditions.
Unfortunately, depending of the type of monitoring to be conducted, tubular mounting of sensors may place significant limitations on the quality of the data obtained. So, for example, flow and resistivity sensors may provide workable data when outfitted at a tubular wall. On the other hand, where the sensor is an acoustic sensor, for example, directed at the formation defining the well, it is unlikely that disposing the sensor at the tubular will result in obtaining any usable formation data. That is, acoustic noise through the tubular and/or downhole fluid flow through the annular space between the tubular and the formation may be quite significant. Thus, the signal to noise ratio acquired by the sensor is unlikely to result in workable data as such relates to the formation. Indeed, such signal to noise ratio issues may present for pressure, electrical, electromagnetic and a variety of other sensor types.
In some cases, where obtaining formation characteristic data is paramount, a subsequent interventional application directed specifically at the formation may be undertaken due to the unavailability of reliable data from a tubular disposed sensor. However, as with the follow-on logging application described above, this may come at significant added costs.
Furthermore, in some cases, the amount of formation characteristic data that is sought across the oilfield is of such significance to operations that cross-well, borehole to surface or surface to borehole logging is undertaken. Cross-well logging involves the acquisition of formation data from multiple wells throughout the oilfield, typically using a source such as a well, surface or shallow dedicated “subsurface” transmitter deployment, with an observation well, surface or dedicated “subsurface” sensor deployment. These methods typically provide a two dimensional plane of information, such as resistivity, between the source and receiver locations. As such, formation characteristics between wells and throughout the oilfield may be better established. Distributing suitable sensors or transceivers into otherwise producing or injecting wells, affords a more comprehensive distribution of detection or transmission “locations” allowing multiple planes of information to be determined, improving areal and vertical coverage of the information.
Of course, formation logging of multiple wells drives up the cost of operations dramatically. That is to say, the interruption and added interventional efforts of follow-on logging are now multiplied. Unfortunately, so are the costs. Due to the added costs associated with follow-on logging, well monitoring often remains limited to that which may be acquired from completions tubular disposed sensors. This may come with sacrifice to the quality of the acquired data, particularly in the case of data sought to be acquired from the formation itself. At present, alternative options for acquisition of such formation data is limited to those options that that are accompanied by the noted dramatic increase in operational costs.